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California/Winged Floater

Anodonta

californiensis/nuttalliana clade

A member of the family Unionidae (freshwater mussels), winged floater is the least common of the Pacific Northwest’s Anondonta species. Five native species of the genus Anodonta occur in western North America, of these three are found in BC. Winged floater, as with other freshwater mussels and clams in BC, is declining in terms of area occupied and number of sites and individuals.

Length Up to 9.5 cm. Smaller than other western Anodonta species, the shell is elliptical and more circular than oval and fairly flat. The outer portion of the shell is yellowish-green, yellowish-brown, or brown, the interior (nacre) is white or bluish. The margin of the rear top of the shell is compressed and raised to form a high prominent wing (though some individuals may be wingless). The valves are very thin but slightly inflated (can be compressed in some individuals). The beak of the winged floater is flattened, not usually raised above the hinge line and contoured with up to 20 irregular single or double-looped concentric ridges. A key lifecycle feature of this and other freshwater mussel species is the need for a host (usually a fish species) to carry the larvae (glochidia). Floaters do not appear to be host specific and in most cases the host species is unknown. Larvae are relatively large, and attach themselves to the fins or gills of their host fish with hook-like projections on each valve. They remain attached to a fish for several weeks (depending on species and water temperature) before letting go and dropping to the bottom where they burrow into the sediment. All Anodonta species have thin fragile shells compared to most other native mussels. This enables them to ‘float’ on less solid substrates like silt and mud. They have also earned their name from colony die-offs that occur from seasonal low oxygen and temperature stress in the summer. The post mortem build-up of gases in the shell cavity may float the light shells to the water’s surface.

A source for authoritative conservation information on thousands of plants and animals and hundreds of ecological communities in BC. From here connect to all provincial and federal recovery plans (including the SARA Registry), COSEWIC (Committee on the Status of Endangered Wildlife in Canada), Identified Wildlife guidance and conservation requirements for specific species and ecological communities of conservation concern impacted by forestry activities) and links to E-Flora and E-Fauna (the Electronic Atlas of the Plants and Wildlife of British Columbia).

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Credits

First edition prepared in 2010 by Pamela Zevit RPBio for the South Coast Conservation Program (SCCP) in partnership with: International Forest Products (Interfor), Capacity Forestry (CapFor). Original funding was made possible through the Sustainable Forestry Initiative (SFI)

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SOUTH COAST CONSERVATION PROGRAM

French translation of SCCP original content available upon request.

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